1. Field of the Invention
The present invention relates to an image pickup device using an image pickup element such as a CCD.
2. Related Background Art
The system of a conventional image pickup device is shown in FIG. 9 which comprised of FIGS. 9A and 9B. Color filters are independently arranged for odd and even fields of interlaced scanning in an image pickup element 101, as shown in FIG. 4. Ye and Cy are read from VOUT1 every other pixel, and Mg and G are read from VOUT2 every other pixel.
Signals of these two systems are sample-held by S/H circuits 102 and 103 and AGC-controlled by AGC circuits 104 and 105, respectively. The AGC-controlled signals are converted into digital signals by analog-to-digital (A/D) converters 106 and 107. These digital signals are subjected to Ye+Mg and Cy+G calculations performed every other pixel in an adder 110 to obtain a luminance signal. Outputs from the A/D converters 106 and 107 are delayed by memories (1Hs) 108 and 109 each having a capacity of one horizontal period (to be referred to as a 1H hereinafter) of a television signal.
Outputs from the memories 108 and 109 are subjected to Ye+Mg and Cy+G calculations performed every other pixel in an adder 111, thereby obtaining a luminance signal. The color carriers of outputs from the adders 110 and 111 are removed by low-pass filters (LPFs) 114 and 115. An output from the low-pass filter 115 is delayed by a memory (1H) 139 having a 1H capacity.
The outputs from the low-pass filters 114 and 115 and the output from the memory 139 constitute continuous 3H luminance signals. The high-frequency components of these signals are removed by a high-pass filter (V-HPF) 140. The noise component of an output from the high-pass filter 140 is removed by a base clip circuit 142 to obtain a vertical aperture signal. The high-frequency component of the output from the low-pass filter 115 is removed by a high-pass filter (H-HPF) 141. The noise component of an output from the high-pass filter 141 is removed by a base clip circuit 143 to obtain a horizontal aperture signal. The vertical and horizontal aperture components are added by an adder 144, and the signal level of the sum from the adder 144 is controlled by a gain control circuit 145, thereby obtaining a detail signal (DTL). An adder 146 adds this detail signal to the output from the low-pass filter 115 which is phase-locked by a delay element (not shown), thereby realizing aperture correction of the luminance signal.
The gain of the high-frequency component of the aperture-corrected luminance signal Y is suppressed by a knee circuit 147. An output from the knee circuit 147 is gamma-corrected by a gamma correction circuit (.gamma.) 148. A blanking signal is added to a gamma-corrected signal in a blanking addition circuit 149. An output from the blanking addition circuit 149 is converted into an analog signal by a digital-to-analog (D/A) converter 150. The analog signal passes through a low-pass filter (LPF) 151 to obtain a video luminance signal YOUT.
The outputs from the memories 108 and 109 are subjected to the coincidence of Ye, Cy, Mg, and G components and the following matrix operation in a first coincidence and matrix circuit 112 to obtain R, G, and B signals as follows: ##EQU1## The gains of the R and B components are controlled by multipliers 118 and 119 in a white balance circuit (WB) with reference to the G component, thereby obtaining a good white balance. The gains of the high-level components are suppressed by knee circuits 120 to 122. Outputs from the knee circuits 120 to 122 are gamma-corrected by gamma correction circuits (.gamma.) 123 to 125. In addition, a second matrix circuit (MTX) 126 performs a matrix operation to generate color difference signals R-Y and B-Y as follows: ##EQU2## for Y=0.3R+0.11B in an NTSC signal
The hue components of these color difference signals are corrected in a hue correction circuit 127, and the high-frequency components of the outputs from the hue correction circuit 127 are removed for later modulation by low-pass filters (LPFs) 128 and 129. A modulation circuit (MOD) 130 performs modulation and adds a burst signal to the input signal. An output from the modulation circuit 130 is converted into an analog signal by a D/A converter 131. This analog signal passes through a low-pass filter (LPF) 132 to obtain a video color signal COUT.
The outputs from the knee circuits 120 to 122 and the gamma correction circuits 123 to 125 are supplied to selectors 133 to 135. The selectors 133 to 135 select the outputs from the knee circuits 120 to 122 or the outputs from the gamma correction circuits 123 to 125 in accordance with whether gamma correction is required. Blanking signals are added to the outputs from the selectors 133 to 135 by blanking addition circuits 136 to 138, thus obtaining a digital red signal ROUT, a digital green signal GOUT, and a digital blue signal BOUT, respectively. These digital outputs are input to a multimedia equipment (not shown) such as a computer or a printer.
In the prior art, the R, G, and B components are obtained by a matrix operation of the outputs from the image pickup element. The horizontal band of the R, G, and B outputs is narrowed in consideration of multimedia applications. When these R, G, and B outputs are supplied to a multimedia equipment such as a computer or a printer, a sufficiently high resolution cannot be obtained, and color blurring undesirably occurs.